1. Field of the Inventnion
The present invention relates to an ink jet recording head forming an image on a recording medium by ejecting an ink and its fabricating method, and to an ink jet recording cartridge having the ink jet recording head and a printer.
2. Description of the Prior Art
As an example of a method for forming an orifice in an ink jet recording head, in particular, a method for forming an orifice of the side-shoot type recording head in which ink is ejected in a direction perpendicular, to the surface of the substrate on which an ink ejection means is installed, it is known to use a metallic plate on which an aperture is formed in a designated position by etching processing, or to make a plate by electroforming. In this method, a substrate having an array of devices used as an ink ejection means and a plate (in this case, a metallic plate) having an array of orifices are formed separately by independent processes, and they are bonded to each other after that processing. Thus in the prior art, in positioning precisely the plates to be bonded to each other, it is possible to have positioning errors, and excess bonding material between plates may enter the orifice of the recording head, which degrades the performance of ejecting ink from the orifice and ultimately leads to a reduction of the quality of recorded images and characters.
In order to solve the above problems, as disclosed in Japanese Patent Application Laying-open No. 169559/1991, what is proposed is an improved method (the so-called "contact mask method") in which, after bonding a plate composed of resin on a substrate (without an aperture), an aperture is formed in the resin layer by applying a laser light through a metallic plate having an aperture which serves as a contact mask.
A prior art technique related to excimer laser processing is described, for example, in Denshi-Zairyou (in Japanese), p. 120, No. 10, 1991. The excimer laser processing has a subsidiary problem in that a conformal mask must be formed separately with respect to the processed materials.
In the processing method proposed in Japanese Patent Application Laying-open No. 169559/1991, any excess bonding material is not found in the processing because no aperture is formed at the time when the substrate and the resin layer are bonded with the bonding material. However, since the metallic plate to be used as a contact mask has an aperture of a designated diameter located at a designated position, the problems relating to an inability to position precisely the metallic plate and the substrate are not overcome. FIG. 1 shows these problems in the prior art.
FIGS. 1A and 1B are cross-sectional views each showing a neighboring area of the orifice for describing a method for forming the orifice in the prior art ink jet recording head. FIG. 1A refers to the state before forming an aperture to be used as an orifice by laser ablation processing, and FIG. 1B refers to the state after completing the aperture.
In FIGS. 1A and 1B, a component 1 is a silicon substrate. A heat generation device 2 used as an ink ejection means and its wiring are located on one face of the silicon substrate 1. An ink fluid route forming member 3 of epoxy resin having a rectangle shape is placed on this face of silicon substrate 1. Below the ink fluid route forming member 3, an ink fluid route 4 is formed as a space extending above the heat generation device 2 on the silicon substrate 1. In addition, in the silicon substrate 1, what is also formed is an ink supply port 5 connected to the ink fluid route 4 and penetrating from one face to the other face of the silicon substrate 1. The ink supply port 5 is generally formed by well known precise processing methods including ultrasonic sand polishing processing, sand-brass processing, and YAG laser processing.
As shown in FIG. 1A, in order to form an aperture to be used as an orifice, a metallic mask 6 having an aperture 6a having a designated diameter is placed near the ink fluid route forming member 3. At this time, in order to establish an ink jet recording head with good ink-ejection performance, it is necessary to control precisely the required position of the aperture 6a of the metallic mask 6 corresponding to the heat generation device 2 on the silicon substrate 1.
However, in practical processing, it is difficult to establish high precision in controlling the position of the aperture 6a of the metallic mask 6 with respect to the heat generation device 2 on the silicon substrate 1. As shown in FIG. 1A, the aperture 3a is formed by removing a resin layer partially corresponding to an open part of the ink fluid route forming member 3 below the aperture 6a laser light Ra exposed through the aperture 6a of the metallic mask 6. So far, even in forming the aperture 3a, namely the orifice 7, as shown in FIG. 1B, the result in shaping the orifice 7 may not be satisfied with the goal for positioning precisely the orifice 7 and the heat generation device 2 in an identical position.
The method of forming the orifice with the excimer laser light is a method requiring additive mechanisms and sub-systems such as an optical system for correcting the energy density distribution, a mask for defining an array of apertures in a designated pattern, and a mechanism for adjusting the positions of the substrate and the projected excimer laser light shining through the mask. With this method, it is difficult to process a large-sized substrate and the operating cost is high in view of the durability of optical components to laser light exposure. Thus, though this kind of method in the prior art uses laser light for processing, the problems described above are found to be common to the mechanical processing of materials which cannot be solved ever in this method.
As for the water resistivity of the surface of the orifice plate which is required to insure durability even in view of contact with the ink fluids, the fabricating method in the prior art has the following problems. In the case where water-resistive resin, in most cases, a fluorine-containing polymer, is coated before an aperture is formed by the laser light exposure, insufficient ablation occurs and hence, excess water-resistive resin remains around the orifice because the water-resistive resin does not absorb the ultraviolet component of the excimer laser light. This leads to an inabiility to eject ink in a designated direction.
In the case that the metallic plating layer 8 having water-resistive property is formed on the surface of the ink fluid route forming member 3 before forming an aperture by the excimer laser light exposure, as shown in FIGS. 2A and 2B, instead of coating water-resistive resin, the intensity of the energy density of the excimer laser is required to be three to ten times as large as in the case of coating water-resistive resin, and in addition, the process for forming an aperture with the laser light having such a strong intensity is accompanied by heat generation, and hence, due to thermal expansion of the orifice plate and the substrate, the required accuracy for shaping the orifice aperture cannot be attained. So, as shown in FIG. 2C, the cross-section of the orifice 7 cannot be shaped in a true circle but is shaped like an oval or even may be shaped in an eccentric circle having concave and convex parts on a peripheral edge of the orifice 7 and on an inner surface thereof.
In addition, what is well known is that, in forming an aperture by the laser light exposure, the horizontal cross-section of the aperture to be formed as an orifice decreases along the laser light path, which means that the shape of the orifice is a tapered hollow cylinder. In this structure of the orifice, the closer the ink comes to the edge of the orifice, the more the velocity of ejected ink is reduced.